Proc. Indian Acad. Sci., Vol. 86 B, October 1977, pp. 255-264, (~ Printed in India. On the functional anatomy of the salivary systems of Purana tigrina Walk. (I-Iomoptera: Cieadidae) DAVID LIVINGSTONE Division of Entomology, Department of Zoology, University of Madras, Post-Graduate Centre, Coimbatore 641 004 MS received 23 May 1977; revised 23 July 1977 Abstract. In Purana tigrina walk. the principal salivary system consists of several digitate lobes which are arranged in two sectors, viz. the cephalic sector and the thoracic sector, corresponding to the anterior and the posterior lobes respectively of the princi- pal salivary gland of a generalised bug. All the lobes of both the sectors are similar in their histology and staining reactions. The accessory salivary system in 1". tigrina is unique among insects. It consists of a very long convoluted, collapsible secretory tube which is more than thirty times longer and six times wider than the accessory salivary duct, the junction of the tube and the duct being indicated by a circlet of five binucleate unicellular gular glands. It is suggested that the tube serves the function of secretion and storage of watery saliva and the gular glands secrete certain material which in combination with the watery saliva, serves as stylet sheath forming material thereby favouring the penetration of the styler fascicle into the hard bark of the stem during feeding operation. The existing fluid pressure in the tube and its collapsible nature are suggestive of the ejection of the fluid through the highly chitinous resistible duct at great force, analogous to the drilling fluid used in mechanical drilling operation. Keywords. Purana tigrina; salivary systems; digitate lobes; functional anatomy; Hemiptera; gular glands; accessory salving tube. 1. Introduction Hemiptera is perhaps the only order of insects whose salivary systems have gained considerable importance. To begin with, only their morphological variations were considered important from the taxonomic point of view (Baptist 1941 and South- wood 1955). But in course of time, when cecidogenesis and the role of sap-suck- ing bugs in cecidogenesis were vigorously pursued, the biochemical and physiological aspects of the different components of the saliva as well as the more intricate mecha- nisms involved in the feeding operation engaged the attention of salivary physio- logists (Miles 1959, 1964,1965, 1967, 1968,1969, 1972; Saxena 1963). Investigations on the formation and function of the watery saliva as well as the stylet sheath materials spared no interest even among insect anatomists in the pursuit of more fundamental and finer details of the salivary systems. Consequently, the literature pertaining to the functional anatomy of the salivary systems of Hemipteroidea in general did not indicate any significant addition. The present paper is an attempt to revive the interest in the functional anatomy of these systems of Hemipteroidea on a compara- tive basis, with a view to assessing their adaptive and evolutionary significance. 255 256 David Livingstone 2. Materials and methods Purana tigrina Walk. is a common cicada found on tree tops in the tropical rain forests of Western Ghats. These bugs derive their sap food from the wood phloem of tall trees. Adult insects were collected during the months of July to October and fixed overnight in warm Bonin's fluid and stored in 80 % methanol. The sa- livary systems of these preserved specimens were dissected out in distilled water and processed for microtome, following the conventional method and serial sections of 6/zm to 8/~m thickness were stained in Ehrlich's haematoxylin-eosin and mounted in balsom. Sections of the salivary systems along with the neuroendocrine system. when stained following Gomeri's chrom alum-haematoxylin-phloxine procedure, showed excellent contrast between the nuclei and the cytoplasmic secretory granules. 3. Results and discussion The salivary systems in P. tigrina, as in most other known Hemiptera, are com- posed of the principal salivary system and the accessory salivary system. Both these systems are morphologically, anatomically and physiologically different from each other and therefore they are treated here as separate systems. 3.1. The principal salivary system The principal salivary system (figure 2) is the main secreting system and its secreting component is the principal salivary gland Which is composed of a large number of secreting units or lobes, arranged in two sectors--viz, the Thoracic sector (TS) and the cephalic sector (CS). Both these sectors, on each side, are connected by the cephalo-thoracic duct (CTD). The cephalic sector has about twelve digitate lobes whereas the thoracic sector has more than twenty such lobes. The lobes of each sector, along with their common duct, are proximally bound by the common con- nective tissue (figure 5). Each digitate lobe differs from the other in size and dis- position and all the lobes vary considerably in length, their diameter ranges from 0"10mm to 0"17mm. The lobes of the cephalic sector of both sides fill the head cap- sule, dorsal to the brain, leaving just enough space for the emergence of the extrinsic muscles of the antennae as well as the ocellar stalk. Similarly, the lobes of the thoracic sector fully occupy the pro-and mesothoracic cavity, filling up the space dorsal to the thoracic ganglionic mass cure-endocrine complex and ventral to the tergal longitudinal muscles and in between the tergo-sternal muscles. A few lobes of this sector run in between the nerve cords that connect the suboeso- phageal ganglion and the thoracic ganglionic mass. All lobes of both the sectors are milk white in colour. Several of them develop a short basal appendage. The lobes of the cephalic sector collectively correspond to the anterior lobe and those of the thoracic sector to the posterior lobe of the principal salivary gland of a generalised bug. Total isolation of the anterior and the posterior lobes and their functional link by a duct is not a regular feature in Hemiptera and it is interesting to recall such an arrangement of the components of the principal salivary glands among aquatic bugs such as Gerrididae and Nepidae (Baptist 1941). The cephalo- thoracic duct has been described in these two aquatic bugs as ' anterior lobe duct '. Salivary systems of Purana tigrina walk. 257 7-v Figures 1-6. (See captions in p. 263) 258 David Livingstone Figures 7-15. (See captions in p. 263) Salivary systems of Purana tigrina walk. 259 The cephalo-thoracic duct, the efferent salivary duct (figure 2 ESD) and the accessory salivary duct (DAS) meet at the ventral aspect of the thoracic sector (figure 5). The efferent duct and the accessory duct meet (figure 4) before they join with the cephalothoracic duct. The efferent salivary duct after leaving the thoracic sector runs forward, meets its fellow of the opposite side at the cervical region and then the common efferent duct enters the salivary syringe which is situated close to the cervix. The histology of the principal salivary gland is the same for all the lobes. Each lobe is enveloped in a thin peritoneal sheath that carries scattered nuclei. The basement membrance is not discernible. The cellular nature of each lobe is also difficult to discern. The entire lobe is compactly filled with a mass of coarsely granular secretory material with several lobate nuclei scattered in the mass. The mass of secretory granules is interspersed with fine canaliculi, carrying homogeneous secretory material. The canaliculi are more prominently visible (figure 3) at the proximal half of each lobe where the secretion that accumulated has already been drained by them. The distal half of each lobe is invariably packed with secretory granules. Tkis suggests that the secretion is drained from the proximal to the distal end of each lobe. The secretion appears to be holocrine. From their staining reaction, no obvious difference in the secretion of the various lobes of the salivary gland can be detected. The lobes of the cephalic as well as the thoracic sectors are similar in that respect. In several other Herniptera, differ- ential secretion of the anterior and posterior lobes of the principal salivary glands has been reported (Baptist 1941; Goodchild 1952; Bronskil et al 1958; Salkeld 1959, 1960; Miles 1959; Livingstone 1967). In the stylet sheath forming Pentatomorph Heteroptera, Miles (1964a, 1964b, 1969) has conclusively reported that the anterior lobe of the ' main' gland secretes the proteinaceous pracursors of the stylet sheath material. The lumen of the efferent salivary duct is uniformly broad (0.02 ram) and is lined with thick chitinous intima. The cephalothoracic duct on the contrary has no inti- real lining at all (figure 3). 3.2. Accessory salivary system The accessory salivary system in P. tigrina is an unique system, consisting of a highly folded and tortuously running tube (figures 6 and 7), a circlet of five binucleate uni- cellular gular glands (figure 9) and an L-shaped accessory salivary duct that joins with the efferent salivary duct at the place of the latter's origin in the thoracic sector of the principal salivary gland. The accessory salivary tube originates somewhere in the thorax. After running haphazardly in between the lobes of the thoracic sector of the principal gland and after investing itself over the rosette of corpus allatum-corpus cardiacum complex (figures 13 and 14) it enters the head capsule. In the head capsule it further takes a winding course in between the lobes of the cephalic sector of the principal salivary gland. Then it approaches the optic lobe and there it makes a number of loops (figures 6 and 7). The junction of the tube and the duct is marked externally by the circlet of unicellular gular glands (figure 12). In length, the accessory salivary tube is over thirty times more than the accessory salivary duct.